This invention relates to an actuating mechanism for a sliding-caliper disc brake having a caliper and an actuator shaft connected to a brake lever which is disposed between one side of the brake disc and the caliper (or an element rigidly connected to the caliper), wherein the axis of the said shaft extends transversely to the axis of the brake disc, wherein an approximately semicylindrical first region of said shaft is supported against the caliper by means of a first partial roller bearing and is thereby rotatable with respect to the caliper by swinging the brake lever, further wherein said shaft carries a projection on its side directed toward the brake disc and away from the first semicylindrical region of the shaft, which projection cooperates, via a rolling element and a second partial roller bearing with a thrust piece which applies force to the brake disc.
In a known mechanism of this type (Eur. Pat. 0,291,071 B1), the projection comprises an eccentric on the actuator shaft which abuts against a rolling element in the form of a rolling plate which is disposed parallel to the plane of the brake disc and which serves to avoid jamming and to reduce sliding friction. The rolling element is supported against the thrust piece via roller bearings. When the brake is actuated, the eccentric carries along the rolling plate against the restoring force of a return spring. If the spring fails, the rolling plate no longer performs its desired function, and upon release of the brake the rolling plate may not be returned to its starting position. Rather, the rolling plate may remain in a radially inner position, and a subsequent actuation of the brake will lead to high sliding friction between the eccentric and the stationary rolling plate. When the brake is actuated, moreover, the position of the contact line of the eccentric changes continuously with respect to the central axis of the thrust piece. This leads to high frictional stresses in the region of the guide means of the thrust piece in the caliper. A further disadvantage from the structural standpoint is the relatively large radial extent of the rolling plate, if it is to withstand high loads, because the extent of the rolling plate depends on the number of rolling elements in the roller bearing.
In order to obviate the above-described unfavorable friction conditions, it is known (Ger. OS 40 32 885) to couple the thrust piece and the actuator shaft via an eccentric antifriction bearing mechanism in the form of a rotational bearing parallel to the axis of rotation of the actuator shaft. While this does improve the friction conditions, the space requirement is substantial, and moreover there is the disadvantage that when the brake lever is actuated the antifriction bearing mechanism undergoes a circular excursion, such that the effects of the forces which develop include undesirable tilting movements of the thrust piece, which movements are difficult to estimate. This leads to nonuniform stressing of the brake linings and hence radial wear, and eventually at maximum braking force the surface stresses are excessive. By mounting the thrust piece to be rotatable in the caliper, using a tubular projection with radial play, during braking the thrust piece can be readily rotatable around the brake axis in response to the circumferential forces, as a result of which disadvantageous bearing stresses occur on the bearing configuration of the eccentric bearings.
A further mechanism as disclosed in German OS 34 11 745 A1 employs an eccentric configuration with the use of a thrust rod; however this arrangement is suitable only for parking brakes. German Pat. No. 2,614,321 C2 discloses the use of a friction-reducing sphere, which results in a mechanism which is unstable and is beset by high sliding friction; and German OSs 31 13 356 A1 and 34 23 875 A1 disclose brake application mechanisms having sliding bearings and comprising thrust pieces which are swingably mounted in the caliper. The swinging movements of the thrust pieces result in disadvantageous radially nonuniform application of the brake lining an undesirable radial wear on the brake lining on the side of the brake disc on which the actuating mechanism is disposed. Further, U.S. Pat. No. 3,830,343 discloses an application mechanism wherein a rotatably mounted cam, which can be acted on by a piston and cylinder unit and which has an involute-shaped contour, acts on a rolling plate which is springably mounted on the lining support. In the event of a failure in the mounting of said plate, the end result can be the same as discussed above in connection with Eur. Pat. 0,291,971 B1. Further, as the brake lining undergoes progressive wear the involute-shaped cam is swung outwardly by means of a one-way coupling, thereby necessitating a large radial installation space. This disadvantage is also seen in the case of the disc brake according to Ger. Pat. No. 2,649,666 C2.